If she did it intentionally, she's a sick and demented mother.
If they were just playing around and the mother put her in because the girl was begging for a ride in one, well, she's a really stupid and ingnorant mother. I don't think you can have much intelligence to not intuitively conclude that placing your daughter in a running washer would be foolhardy and dangerous.
So either way, there's no defending her actions. Unless the child crawled in when she wasn't looking. But the video footage shows her putting the child in one, then moving her to a front-loading washer. So that rules out any form of "accident."